Bound-state electrons synergy over photochromic high-crystalline C3N5 nanosheets in enhancing charge separation for photocatalytic H2 production

Solar-driven water splitting for photocatalytic hydrogen evolution is considered a highly promising and cost-effective solution to achieve a stable renewable energy supply. However, the sluggish kinetics of electron-hole pairs’ separation poses challenges in attaining satisfactory hydrogen production efficiency. Herein, we synthesized the exceptional performance of highly crystalline C 3 N 5 (HC–C 3 N 5 ) nanosheet as a photocatalyst, demonstrating a remarkable hydrogen evolution rate of 3.01 ​mmol ​h −1 ​g −1 , which surpasses that of bulk C 3 N 5 (B–C 3 N 5 ) by a factor of 3.27. Experimental and theoretical analyses reveal that HC-C 3 N 5 nanosheets exhibit intriguing macroscopic photoinduced color changes, effectively broadening the absorption spectrum and significantly enhancing the generation of excitons. Besides, the cyano groups in HC-C 3 N 5 efficiently captures and converts photoexcited electrons into bound states, thereby prolonging their lifetimes and effectively separating electrons and holes into catalytically active regions. This research provides valuable insights into the establishment of bound electronic states for developing efficient photocatalysts. A photochromic HC-C 3 N 5 nanosheet was synthesized by utilizing an alkaline potassium salt-assisted high-crystallization approach. Under the synergistic cooperation of bound-state electrons, photochromic nature and increased crystallization, HC-C 3 N 5 demonstrates a remarkable photocatalytic hydrogen evolution rate and long-term durability under the full-spectrum irradiation. • HC-C 3 N 5 nanosheets with photochromism were initiatively synthesized by alkaline potassium salt heat polymerization method; • Photochromic HC-C 3 N 5 demonstrated switch to darker shades, extending the absorption spectrum and facilitating carrier excitation; • Bound electrons in HC-C 3 N 5 can direct towards the vicinity of active sites and enable better interaction with protons.